The present invention relates to a method for the dehalogenation of an alpha halogenated carbonyl compound or in some instances to the prevention of the formation of such alpha halogenated carbonyls from the corresponding non-halogenated carbonyls. The word "dehalogenation" as used herein is meant to include both complete dehalogenation as well as a mere reduction in the degree of halogenation. Further, "dehalogenation" as used herein involves the replacement of the halogen ions with hydrogen ions, and does not include dehydrohalogenation.
There are many instances wherein it may be desirable to dehalogenate an alpha halogenated carbonyl compound, that is to replace the alpha halogen atoms with hydrogen atoms. In some instances where there is more than one alpha halogen atom present, the dehalogenation desired may merely be from a high degree of halogenation to a lower degree of halogenation, such as the dehalogenation of a tri-halogenated aldehyde to form a di-halogenated aldehyde; or it may be desired to effect complete dehalogenation such as the conversion of a tri-halogenated aldehyde to the corresponding non-halogenated aldehyde. The desire to effect the dehalogenation may sometimes arise because the halogenated carbonyl compound is an undesirable by-product of a chemical process, in which instance the same net results may usually be accomplished by merely suppressing the formation of the halogenated carbonyl.
For example, there is a well known conversion process for the conversion of an alkene to an aldehyde (such as ethylene to acetaldehyde) wherein in a first stage the alkene is reacted with an aqueous acidic solution of an oxidant catalyst system comprising a noble metal together with a redox agent comprising cupric chloride, the aldehyde then being separated from the spent catalyst solution which is in a chemically reduced form. The spent catalyst solution is then reoxidized with a source of molecular oxygen (typically air) before being recycled to the first stage of the process for the conversion of additional quantities of alkene. Such a process is described, for example, in a paper by Dr. J. Smidt in "Chemistry And Industry" (Jan. 13, 1962), pages 54-61. In such conversion process, a continuing problem has been that in addition to the production of the desired non-halogenated aldehyde product, there is also produced minor amounts of chloroaldehydes. These chloroaldehydes represent a product loss and therefore a satisfactory method for dehalogenating them to the desired non-halogenated aldehyde is desired so as to improve the overall yield. Further, from an ecological standpoint the dehalogenation of these chloroaldehydes is desirable since disposal of halogenated compounds presents environmental problems.
The foregoing is just one example of an industrial process where the dehalogenation of a halogenated carbonyl compound is desired although there are numerous other situations where such is obviously desirable. It is thus an object of the present invention to provide a process for the dehalogenation of alpha halogenated compounds, including complete dehalogenation of the alpha halogens, as well as, when treating a halogenated carbonyl compound having more than one alpha halogen, the replacement with hydrogen of less than all the alpha halogens. It is a particular object of the present invention to provide a process for the dehalogenation of the chlorinated acetaldehydes. From the description of the foregoing alkene conversion process, it may be recognized that the necessity for dehalogenation in that particular process is brought about by an undesirable halogenation, and thus in such particular process the same net result, that is production of a non-halogenated aldehyde product free of contamination by halogenated derivatives, could be accomplished by the prevention of the halogenation in the first instance. The inventor's discovery disclosed herein allows such to be accomplished and the accomplishment of such is an additional object of the invention.